The gravure printing is one kind of the intaglio printing and is characterized in that print having a fine gradation can be obtained in multi-color or mono-color printing, as is well known to those skilled in the art.
Prior to actual printing with use of the gravure printing machine, color matching of ink is done usually. Color matching includes a proofing process with use of spatula application.
This proofing process is done conventionally in such a manner as follows; first a skilled person determines compound of the target color according to his sense referring a proof print of primary color ink, compounds ink actually, then applies said ink on a printing plate with a spatula and makes a proof print and, finally, decides pass or fail by observing the proof print. If failed, the ink is recompounded by adding primary color ink and is decided pass or fail by observing the proof print with use of the ink recompounded. Such compounding is repeated until pass-decision is obtained.
Such manual color matching as mentioned above has disadvantages as follows;
(a) Since color difference between the color of the proof print and the target color is decided only by observation, different decisions may be obtained according to the senses of the skilled persons in charge and, accordingly, there caused such troubles that printed products are refused to accept by the person who ordered printing thereof.
(b) Since the ink is applied on the printing plate manually with use of the spatula on proof printing, proofing conditions such as applying speed and pressure are varied slightly at every proof printing. Namely, reproductive stability thereby is inferior.
Contrary to the above, color matching method with use of computer has been proposed into which recent developments in the field of the chromatology are introduced.
In this method, tristimulus values X, Y, Z of the target color are obtained by measuring spectroscopic reflection factors of the target color in the visible light zone and the luminosity index L and chromaticness indexes a, b in the Lab space are calculated based upon the tristimulus values X, Y, Z. Those indexes about the target color are stored into the memory of the computer. Also, the luminosity index L' and chromaticness indexes a', b' about the color obtained by proof-printing with use of the ink having been compounded are calculated. The color difference is calculated by comparing these indexes L' a', b' about the color of the proof print with those L, a, b about the target color and the ink is recompounded based upon the color difference obtained. According to the method, the problem (a) above mentioned is dissolved.
Moreover, there has been known an automatic proof printing machine being capable of printing under constant printing conditions.
This machine has a cylindrical press drum on the peripheral surface of which a material to be printed thereon is fixed. On proof printing, the press drum is moved in contact with the printing plate by a reversible electric motor.
However, the conventional proof-printing machine of this type has disadvantages in that it is impossible to obtain high acceleration and/or deceleration on driving the press drum, that it is impossible to obtain high velocity within a short distance, that it is difficult to obtain an objective velocity exactly and that only an inferior reproductive stability can be obtained.